A flat panel display such as a liquid crystal display and a plasma display is widely applied to from a mobile device such as a cellular phone terminal to a large device such as a public display set up on the street. Much of the development of such a display emphasizes on wide viewing angle, high brightness, and high image quality, and a clean and clear display from any angle has been requested.
Meanwhile, there is content such as secret information and private data displayed on the display that one does not want someone else to see. Therefore, in today's progressing ubiquitous society accompanied by the development of information devices, it is also an important problem to prevent other people from seeing the display content in public where unspecified people exist.
Furthermore, secret information is sometimes handled in office, information that one does not want a person who passes behind the seat to see.
In some of the cellular phone terminals and the like, an optical shield plate (louver) is installed, and a display is provided in which the display content can be visually checked only from a specific direction. However, since the display content can be peeped from right behind the user, the display is not satisfactory in terms of confidentiality.
An example of a related art for solving the problems includes “Image Display Device” disclosed in Patent Document 1. In the image display device, the user wears spectacles with image selecting function, and only the person wearing the spectacles (user) can visually check a specific image (hereinafter, “secret image”), while another image (hereinafter, “public image”) is presented to other people.
Specifically, an image forming device shown in FIG. 1 stores an input image signal 11 of one frame to an image information storing memory 12 based on a frame signal 13. The image forming device then reads out image information from the memory 12 at a speed twice as fast as the frame cycle (i.e., reads out twice during one frame time), compresses in half the signal read out first, inputs the signal to a synthetic circuit 15 as a first image signal 14, converts the saturation and the luminance of an image signal read out next, and inputs the signal to the synthetic circuit 15 as a second image signal 17. Therefore, the image display unit 18 alternately displays the first image signal 14 and the second image signal 17.
Meanwhile, the frame signal 13 is also inputted to a spectacle shutter timing creating circuit 19. The spectacle shutter timing creating circuit 19 drives a shutter of spectacles 21 and controls the spectacle shutter so that the user cannot see an image based on the second image signal 17.
According to the configuration and the operation, a person not wearing the spectacles 21 can see a gray image or a third image (public image) that is a synthetic image of the first image signal 14 and the second image signal 17 and that is not related to the first image signal 14, and a person wearing the spectacles 21 can see a desired image (secret image) based on the first image signal 14.
Another example of a related art for solving the problems includes “Method for Providing Data That Can Be Seen Privately on Display That the Public Can See” disclosed in Patent Document 2. The method disclosed in Patent Document 2 allows only an authorized user to decipher a private image (secret image) on the display and allows an unauthorized user to see only a public image such as a random pattern, an image difficult to decipher, or a screen saver image.
To promote the object, the invention disclosed in Patent Document 2 synchronizes an image processing technique including a data hiding pattern and an alternating pattern with a display incorporated with an image created by an image processing technology (for example, combined with a wearable device such as active glasses). Finally, ability for providing data that can be seen privately on display that the public can see is completed by a “known ability for integrating dissimilar images into a single image” of the visual system of human beings.
Another example of a related art for solving the problems includes a “Secret Mechanism” disclosed in Patent Document 3. To prevent a third party from identifying the display content of a display device of a word processor, a computer, or the like, the secret mechanism disclosed in Patent Document 3 displays a display pattern such as characters or graphics on a pattern display unit of the display device and displays an incomprehensible disturbance pattern (characters or graphics for preventing a third party from identifying characters or graphics displayed as a display pattern). A switching signal outputting unit creates a switching signal synchronized with the display timing of the display pattern and the disturbance pattern and provides the signal to spectacles. The spectacles open and close the shutter in accordance with the switching signal, and only the user of the display device can see the display pattern. A nonuser sees the display pattern and the disturbance pattern switched at high speed at the same time and cannot identify the display content due to the afterimage effect of the display screen.
The secret mechanism disclosed in Patent Document 3 also divides the display pattern (secret image) into a plurality of patterns to create a divided display pattern and further divides the disturbance pattern (public image) into a plurality of patterns to create a divided disturbance pattern to thereby make it more difficult for a nonuser to recognize the display pattern.
Furthermore, examples of a related art for creating a plurality of transformed images from one image that are different from the original image include “Contaminant Content Distribution System, Contaminant Content Distribution Apparatus, Contaminant Content Utilizing Apparatus, Contaminant Content Distribution Method, and Contaminant Content Utilization Method” disclosed in Patent Document 4 and “Image Processing Method, Apparatus, and Recording Medium Recording Image Processing Program” disclosed in Patent Document 5.
Patent Document 1: Japanese Patent Laid Open Publication No. 63-312788
Patent Document 2: Japanese Patent Laid Open Publication No. 2001-255844
Patent Document 3: Japanese Patent Laid Open Publication No. 6-186503
Patent Document 4: Japanese Patent Laid Open Publication No. 2001-16429
Patent Document 5: Japanese Patent Laid Open Publication No. 2002-72994